Attempts are being made to treat atherosclerosis in symptomatic adults by interfering with recognized risk factors. Because the obstructive fibrous plaques of atherosclerosis in adults are suspected to result from progression of fatty streaks that developed during childhood, the question has now been raised whether it might not be easier to prevent symptomatic disease in adulthood by stopping the progression of fatty streaks in children. We are studying whether fatty streaks are indeed the precursors of fibrous plaques, and if so, which are the factors that cause their progression to fibrous plaques. We are seeking to identify factors responsible for initiating fibrous plaque formation, and factors that influence greater fibrous plaque development in certain arterial segments. We have available for study the coronary arteries and the aortas of infants, children, adolescents, and young adults (up to and including 25 years of age). We are approaching our objectives by using correlative electron microscopy and chemical lipid analysis. By morphological means we are trying to determine the types of cells and their lipid content, and, by chemical means, the total lipid content and lipid composition of fatty streaks of different arterial segments and of different age groups. Through those methods we attempt to identify those factors that are associated with the formation of fibrous plaques.